Use of IMSI during femtocell registration to avoid identifier conflicts

ABSTRACT

A method and system is disclosed for including an IMSI in an EVDO access request. When an access terminal determines that any access request it makes will be sent to a micro-type base station, the access terminal will include its IMSI in any EVDO access request. When a micro-type base station receives an EVDO access request containing an IMSI of the requesting access terminal, the micro-type base station will use the included IMSI to establish and identify a data connection to a PDSN.

BACKGROUND

In a typical cellular radio communication system (wireless communicationsystem), an area is divided geographically into a number of cell sites,each defined by a radio frequency (RF) radiation pattern from arespective base transceiver station (BTS) antenna. The base stationantennas in the cells are in turn coupled to a base station controller(BSC), which is then coupled to a telecommunications switch or gateway,such as a mobile switching center (MSC) and/or a packet data servingnode (PDSN) for instance. The switch or gateway may then be coupled witha transport network, such as the PSTN or a packet-switched network(e.g., the Internet).

A subscriber (or user) in a service provider's wireless communicationsystem accesses the system for communication services via an accessterminal, such as a cellular telephone, pager, or appropriately equippedportable computer, for instance. When an access terminal is positionedin a cell, the access terminal (also referred to herein by “AT”)communicates via an RF air interface with the BTS antenna of the cell.Consequently, a communication path or “channel” is established betweenthe AT and the transport network, via the air interface, the BTS, theBSC and the switch or gateway.

Functioning collectively to provide wireless (i.e., RF) access toservices and transport in the wireless communication system, the BTS,BSC, MSC, and PDSN, comprise (possibly with additional components) whatis typically referred as a Radio Access Network (RAN). In practice, theRAN may be organized in a hierarchical manner, with multiple BTSs underthe control of a single BSC, multiple BSCs linked to a single MSC, andmultiple MSCs in one region or metropolitan area connecting to RANs inother regions or metropolitan areas by way of gateway MSCs or otherinter-regional switches.

As the demand for wireless communications has grown, the volume of calltraffic in most cell sites has correspondingly increased. To help managethe call traffic, most cells in a wireless network are usually furtherdivided geographically into a number of sectors, each definedrespectively by radiation patterns from directional antenna componentsof the respective BTS, or by respective BTS antennas. These sectors canbe referred to as “physical sectors,” since they are physical areas of acell site. Therefore, at any given instant, an access terminal in awireless network will typically be positioned in a given physical sectorand will be able to communicate with the transport network via the BTSserving that physical sector.

The functional combination of a BTS of a cell or sector with a BSC iscommonly referred to as a “base station,” although the actual physicalconfiguration can range from an integrated BTS-BSC unit to a distributeddeployment of multiple BTSs under a single BSC, as described above.Regardless of whether it is configured to support one cell, multiplecells, or multiple sectors, a base station is typically deployed toprovide coverage over a geographical area on a scale of a few to severalsquare miles and for tens to hundreds to several thousands (or more) ofsubscribers at any one time. On this scale, coverage is referred to as“macro-network coverage” and the base station is referred to as a“macro-type base station.”

More recently, a type of base-station functional unit aimed at coverageover a much smaller physical area and at concurrent support of manyfewer subscribers has been introduced. Referred to generically herein asa “micro-type base station,” this device, roughly comparable in size todesktop phone, can operate to fill in gaps in macro-network coverage(e.g., in buildings), as well as provide limited and exclusive coverageto individual subscribers within residential (or other small-scale)spaces. As such, macro-network service providers have begun offeringmicro-type base stations as consumer devices, under the more technicalmoniker of “femtocell.” In addition to “femtocell,” other terms for amicro-type base station used interchangeably herein include “femto basestation,” “femto BTS,” “picocell,” “pico BTS,” “microcell,” “micro BTS,”and “Low-Cost Internet Base Station” (“LCIB”). The prefixes “femto,”“pico,” and “micro” are also used herein to refer correspondingly torespective coverage areas. Note that “low-cost” is not intended to belimiting; that is, devices of any cost may be categorized as LCIBs,although it may be expected that most LCIBs will typically be lessexpensive on average than most macro-network base stations.

A typical femtocell may be considered to be essentially a low-power,low-capacity version of a macro-type base station, providing the same RFinterface for wireless access, only for a much smaller physical coveragearea. However, instead of connecting directly to an MSC, PDSN, othernetwork switch, a femtocell communicates with the service provider'snetwork via one or another form of broadband connection associated withor available to the consumer-owner (or renter) of the femtocell. Withrespect to a subscriber's wireless access, the small coverage area of afemtocell is viewed by the wireless communication system in the samemanner as any other macro coverage area (e.g., cell or sector). Inparticular, a subscriber may move between neighboring coverage areas ofmacro-type base stations and femtocells, and even between neighboringcoverage areas of different femtocells, in the same way the subscribermoves between neighboring macro coverage areas.

More specifically, as a subscriber at an access terminal moves betweenwireless coverage areas of a wireless communication system, such asbetween cells, sectors, or femto coverage areas, or when networkconditions change or for other reasons, the AT may “hand off” fromoperating in one coverage area to operating in another coverage area. Ina usual case, this handoff process is triggered by the access terminalmonitoring the signal strength of various nearby available coverageareas, and the access terminal or the BSC (or other controlling networkentity) determining when one or more threshold criteria are met. Forinstance, the AT may continuously monitor signal strength from variousavailable sectors and notify the BSC when a given sector has a signalstrength that is sufficiently higher than the sector in which the AT iscurrently operating. The BSC may then direct the AT to hand off to thatother sector. By convention, an AT is said to handoff from a “source”cell or sector (or base station) to a “target” cell or sector (or basestation).

In some wireless communication systems or markets, a wireless serviceprovider may implement more than one type of air interface protocolwithin a single system. For example, a carrier may support one oranother version of CDMA, such as EIA/TIA/IS-2000 Rel. 0, A (hereafter“IS-2000”) for both circuit-cellular voice and data traffic, as well asa more exclusively packet-data-oriented protocol such as EIA/TIA/IS-856Rel. 0, A, or other version thereof (hereafter “IS-856”). In such a“hybrid system,” an access terminal might not only hand off betweencoverage areas under a common air interface protocol (e.g., betweenIS-2000 sectors) but may also hand off between the different airinterface protocols, such as between IS-2000 and IS-856. An accessterminal capable of communicating on multiple air interface protocols ofa hybrid system is referred to as a “hybrid access terminal.” Handoffbetween different air interface protocols (or, more generally, betweendifferent access technologies) is known as “vertical” handoff.

OVERVIEW

When a subscriber at an access terminal initiates a call or data sessionvia the RAN, one or another authentication and authorization procedureis carried out to verify the identity of the subscriber and validate thepermissions and privileges required for the requested service.Typically, some form of identifier of the access terminal is used in theprocedure, and becomes associated with the call or data sessionestablished as a result of the initiation process. The specificidentifier depends on the type of session being created and the airinterface protocol under which the session request is made, among otherpossible factors.

In particular, when an AT requests a data connection under IS-2000, itincludes an “International Mobile Subscriber Identifier” (“IMSI”) in therequest. The BSC receiving the request then uses the IMSI in the requestto establish and identify a segment or “leg” of the data connectionbetween the BSC and a PDSN. When a request for a data connection is madeunder IS-856, the AT includes an “Electronic Serial Number” (“ESN”) inthe request, but not the IMSI. In this case, the BSC uses the ESN fromthe request in a transaction with an “Access NodeAccounting-Authentication-Authorization” (“AN-AAA”) server in order(among other purposes) to determine a unique IMSI associated with theESN (and thereby, with the AT). The BSC then uses the IMSI acquired fromthe server to establish and identify the segment of the data connectionbetween the BSC and a PDSN.

In a typical RAN deployment comprising macro-type base stations, thenumber of BSCs that require a connection to the AN-AAA server can be onthe order of tens to hundreds (or more), but is generally well within arange that the server can accommodate. The server may actually beimplemented according to a distributed architecture in which multipleserver nodes each maintain a relatively few connections to differentsets of the BSCs. In either case, the aggregate of all the connectionsbetween the BSCs and the server (or server nodes) does not represent apractical limitation with respect to system deployment. Consequently,the transaction between a BSC to the server to resolve an ESN to an IMSIas part of data-session setup under IS-856 is routinely supported.

The introduction of femtocells can significantly alter the number ofbase stations requiring connections to the AN-AAA server. Specifically,since femtocells integrate the functionality of a BSC and are (at leastto some extent) marketed as consumer devices, the number of femtocellsthat could attempt to access the AN-AAA server will scale roughly likethe number (or some sizeable fraction thereof) of subscribers of aservice provider. Because this number generally exceeds the number ofindividual BSCs that can connect to the AN-AAA server, femtocells areconfigured to operate without a connection to the AN-AAA server. Moreparticularly, when a femtocell receives a request from an AT for a datasession under IS-856, the femtocell assigns an IMSI to the AT for therequested data session and uses the assigned IMSI to identify thesegment of the data connection between the femtocell and the PDSN. Inpractice, the assigned IMSI is one of a pool of assignable IMSIsmaintained at the femtocell.

While local assignment of an IMSI by a femtocell for IS-856 datasessions addresses the absence of a connection between the femtocell andthe AN-AAA server, there is generally no guarantee that two or morefemtocells connected to the same PDSN will choose unique IMSIs when eachof the two or more femtocells makes such a local assignment. Since thePDSN identifies its data connections to a BTS or femtocell according toan IMSI, a conflict or “collision” of data connection identifiers canoccur at a PDSN when two or more femtocells connected with the PDSNassign identical IMSIs to different respective data connections at thesame time. This problem tends to be exacerbated by the potentially largenumber of femtocells that can connect to a PDSN at any one time.

Accordingly, embodiments of the present invention provide a method andsystem for providing a unique IMSI in an access request from an accessterminal to a base station for an IS-856 data session when omitting theIMSI from the access request could otherwise lead to an IMSI collisionat a PDSN or other network switch. More specifically, an AT will includeits IMSI in an IS-856 access request to a base station when the ATdetermines that the base station is a femtocell. Additionally, afemtocell that receives an IS-856 access request containing an IMSI willuse the IMSI to establish and identify a data connection to a PDSN,instead of locally assigning an IMSI. Advantageously, multiplefemtocells connected to a common PDSN may establish different IS-856data sessions with unique IMSIs, even when each femtocell lacks aconnection to the AN-AAA server.

Hence, in one respect, various embodiments of the present inventionprovide, in an access terminal configured to operate in a wirelesscommunication system that includes at least one micro-type base station,a method comprising: the access terminal operating in a first idle statein which at least: (i) the access terminal includes a particularidentifier in any given access request for a data connection of a firstprotocol type, the particular identifier being uniquely associated withthe access terminal and being required by the first protocol to beincluded in access requests for data connections of the first protocoltype, and (ii) the access terminal omits the particular identifier inany given access request for a data connection of a second protocoltype, the particular identifier not being specified by the secondprotocol to be included in access requests for data connections of thesecond protocol type; while operating in the first idle state, theaccess terminal making a first determination that any access request itmakes will be sent to a micro-type base station; and based at least onthe first determination, transitioning to operating in a second idlestate in which at least: the access terminal includes the particularidentifier in any given access request for a data connection of thesecond protocol type.

In another respect, various embodiments of the present inventionprovide, in a micro-type base station configured to operate in awireless communication system, and further configured to support dataconnections of both a first protocol type and a second protocol typewith access terminals operating in the wireless communication system, amethod comprising: receiving an access request for a data connection ofthe second protocol type from an access terminal, the access requestincluding a particular identifier that is uniquely associated with theaccess terminal, and the second protocol type not specifying theparticular identifier to be included in access requests for dataconnections of the second protocol type; and establishing a datacommunication session of the second protocol type with the accessterminal based at least in part on the particular identifier included inthe access request.

In still another respect, various embodiments of the present inventionprovide an access terminal configured to operate in a wirelesscommunication system that includes at least one micro-type base station,the access terminal comprising: means for operating in a first idlestate in which at least: (i) the access terminal includes a particularidentifier in any given access request for a data connection of a firstprotocol type, wherein the particular identifier is uniquely associatedwith the access terminal and is required by the first protocol to beincluded in access requests for data connections of the first protocoltype, and (ii) the access terminal omits the particular identifier inany given access request for a data connection of a second protocoltype, wherein the particular identifier is not specified by the secondprotocol to be included in access requests for data connections of thesecond protocol type; means for making a first determination that anyaccess request the access terminal makes will be sent to a micro-typebase station; and means for, based at least on the first determination,transitioning to operating in a second idle state in which at least: theaccess terminal includes the particular identifier in any given accessrequest for a data connection of the second protocol type.

In yet another respect, various embodiments of the present inventionprovide a micro-type base station configured to operate in a wirelesscommunication system, and further configured to support data connectionsof both a first protocol type and a second protocol type with accessterminals configured to operate in the wireless communication system,the micro-type base station comprising: means for receiving an accessrequest for a data connection of the second protocol type from an accessterminal, wherein the access request includes a particular identifierthat is uniquely associated with the access terminal, and wherein thesecond protocol type does not specify the particular identifier to beincluded in access requests for data connections of the second protocoltype; and means for establishing a data communication session of thesecond protocol type with the access terminal based at least in part onthe particular identifier included in the access request.

These as well as other aspects, advantages, and alternatives will becomeapparent to those of ordinary skill in the art by reading the followingdetailed description, with reference where appropriate to theaccompanying drawings. Further, it should be understood that thissummary and other descriptions and figures provided herein are intendedto illustrate the invention by way of example only and, as such, thatnumerous variations are possible. For instance, structural elements andprocess steps can be rearranged, combined, distributed, eliminated, orotherwise changed, while remaining within the scope of the invention asclaimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart depicting an example embodiment of a method ofusing an IMSI in a data session request to a micro-type base station.

FIG. 2 is a state diagram illustrating an example embodiment of using anIMSI in a data session request to a micro-type base station.

FIG. 3 is a simplified block diagram of a wireless communication systemin which an example embodiment of a method of using an IMSI in a datasession request to a micro-type base station could be carried out.

FIG. 4 illustrates an example embodiment of logical steps forimplementing in an AT a method of using an IMSI in a data sessionrequest to a micro-type base station.

FIG. 5 illustrates an example embodiment of logical steps forimplementing in a micro-type base station a method of using an IMSI in adata session request to a micro-type base station.

FIG. 6 is a block diagram of an example access terminal in which usingan IMSI in a data session request to a micro-type base station may beimplemented.

FIG. 7 is a block diagram of an example base station in which using anIMSI in a data session request to a micro-type base station may beimplemented.

DETAILED DESCRIPTION

The present invention will be described by way of example with referenceto Code Division Multiple Access (“CDMA”) communications in general, andto IS-2000 and IS-856 communications in particular. As described below,IS-2000 applies to both circuit-cellular and packet-data communications,and is referred to herein as “conventional” CDMA communications. IS-856applies more exclusively to packet-data communications (including, e.g.,real-time voice and data applications), and is referred to herein as“high rate” packet-data communications. Under IS-2000, packet-datacommunications are conventionally referred to as “1X-RTT”communications, also abbreviated as just “1X.” Packet-datacommunications under IS-856 are conventionally referred to as “EV-DO”communications, also abbreviated as just “DO.” It should be understoodthat the present invention can apply to other wireless voice and dataprotocols including, without limitation, IS-95 and GSM, which, togetherwith IS-2000 and IS-856 are considered herein, individually or in anycombination, to comprise a CDMA family of protocols.

FIG. 1 is a flowchart depicting an example embodiment of a method forproviding a unique IMSI in an access request from an access terminal toa base station for an IS-856 data session. By way of example, the stepsof the flowchart could be implemented in an access terminal in awireless communication system that includes a macro-type base stationand a micro-type base station (among other elements of a RAN), and thatoperates according to a CDMA family of protocols, including IS-856. Asdescribed above, a macro-type base station may then be taken to comprisea cell and/or sector BTS under the control of a BSC and configured tooperate according to a CDMA family of protocols, including at least1X-RTT and EVDO, while a micro-type base station may be considered afemtocell.

At step 102, the access terminal operates in a first idle state in whichat least: (i) the access terminal includes a particular access-terminalidentifier in any given access request for a data connection of a firstprotocol type, and (ii) the access terminal omits the particularaccess-terminal identifier in any given access request for a dataconnection of a second protocol type. In an idle state, such as thefirst idle state, the AT is not engaged in an active call or datasession via any base station. Rather the AT monitors a paging channel(or other reverse-link control channel) for messages from the RAN,including messages alerting of an incoming call. The AT can alsoinitiate a call or data session (e.g., in response to a user/subscriberinstruction via an input interface of the AT) by sending an accessrequest to a base station. In practice, the AT may send multiple accessrequests in order to initiate and (ultimately) establish a data sessionvia a base station. However, for the purposes of the discussion herein,the term “access request” will be understood to encompass one or moreaccess requests transmitted to the RAN in order to initiate andestablish a call or data session.

In accordance with the example embodiment, the AT can initiate datasessions of at least a first protocol type and a second protocol type bysending an appropriate access request to a base station. For a datasession of the first protocol type, the access request must, accordingto the first protocol, include the particular access-terminalidentifier, while for a data session of the second protocol type, theaccess request is not specified as including the particularaccess-terminal identifier. More specifically, the particularaccess-terminal identifier is uniquely associated with the accessterminal and is required by the first protocol to be included in accessrequests for data connections of the first protocol type. Further, theparticular access-terminal identifier is not specified by the secondprotocol to be included in access requests for data connections of thesecond protocol type. The first idle state characterizes one set ofbehaviors of the AT with respect to access requests for data connectionsof either protocol type.

In further accordance with the example embodiment, the first protocoltype is 1X-RTT and the second protocol type is EVDO. Hence a datasession of the first protocol type is a 1X-RTT data session, while adata session of the second protocol type is an EVDO data session. Alsoin accordance with the example embodiment, the particularaccess-terminal identifier is a unique IMSI. In practice, IMSIs can beassigned by a service provider (e.g., owner/operator of the wirelesscommunication system) to ATs associated with subscribers of the serviceprovider. A unique IMSI is one that is assigned to only one subscriberaccess terminal at any given time. To the extent that different serviceproviders have non-overlapping groups of IMSIs available to assign, aunique IMSI is one that is unique across all of the different serviceproviders.

In conventional operation, a unique IMSI is required in access requestsfor 1X-RTT data sessions, but is not specified in IS-856 as a parameterin access requests for EVDO data sessions. As described below in moredetail, both types of data sessions typically include a data-pathsegment (or “leg”) comprising a data connection between the base stationand a PDSN. The PDSN identifies this data connection according to anIMSI associated with the AT. For a 1X-RTT data session, a unique IMSI isprovided in the initiating access request(s) by the AT as a matter ofprotocol, and is thereby supplied to the PDSN as a unique identifier forthe data connection to the base station. For an EVDO data session,however, the AT does not conventionally include a unique IMSI in theaccess request(s), but rather provides a different identifier, namely anESN. A base station, and more particularly a macro-type base station,receiving this access request generally resolves the ESN into a uniqueIMSI as part of an authentication and authorization transaction with theAN-AAA server. Thus, the PDSN again is supplied with a unique IMSIidentifying the data connection to a macro-type base station for an EVDOdata session, even though an IMSI is not (by protocol convention)included in the access request(s). Accordingly, the behavior of the AToperating in the first idle state of step 102 accommodates setup of both1X-RTT and EVDO data sessions, wherein for either type of data sessionthe data connection between a macro-type base station and the PDSN has aunique IMSI identifier.

At step 104, while operating in the first idle state, the accessterminal makes a determination that any access request it makes will besent to a micro-type base station. In accordance with the exampleembodiment, the AT could make the determination by selecting aparticular base station from which to seek access, and recognizing thatan identifier of a particular base station is indicative of a micro-typebase station. More specifically, an AT operating in an idle state mayhand off from one base station to another; i.e., from a source basestation to a target base station, as described above. As part of thehandoff procedure, the AT acquires system information about the targetbase station, including some form of identifier. The AT may in turndetermine that the identifier is one known to be associated with amicro-type base station. If the AT then seeks access from the targetbase station, the AT will have determined that it will be sending anaccess request to a micro-type base station.

For instance, under a CDMA family of protocols, including IS-2000 andIS-856, the AT can receive a “Systems Parameter Message” from a targetbase station (or cell or sector) after a handoff. As is known, a SystemsParameter Message includes a “Network ID” (“NID”) for the target basestation. In accordance with the example embodiment, the service providercould configure the wireless communication system so that a certainrange (or ranges) of NID values are reserved for femtocells (or othermicro-type base stations), while another range (or ranges) of NID valuesare reserved for macro-type base stations. The AT will maintain thisrange information, and will thus be able to identify any given basestation as either a femtocell (or other micro-type base station) or amacro-type base station according to the given base station's NID.

At step 106, based at least on the determination of step 104, the ATtransitions to operating in a second idle state in which at least: theaccess terminal includes the particular access-terminal identifier inany given access request for a data connection of the second protocoltype. As in the first idle state, in the second idle state the AT is notengaged in an active call or data session via any base station. Again,the AT will monitor its paging channel and can initiate a call or datasession by issuing an access request. However, unlike the first idlestate, the second idle state is characterized (at least) in that the ATnow includes the particular access-terminal identifier in any givenaccess request for a data connection of the second protocol type.

In accordance, again, with the example embodiment the second protocoltype is EVDO and the access-terminal identifier is a unique IMSI. Thus,when operating in the second idle state, the AT will now include itsunique IMSI in access requests for EVDO data sessions, contrary toconventional protocol for EVDO access requests. Since the ATtransitioned to the second idle state based on the determination that itwould be sending any access requests to a femtocell (or other form ofmicro-type base station), the operational behavior of the second idlestate ensures that femtocells will receive unique IMSIs in accessrequests from the AT for EVDO data sessions. The advantage of theoperational behavior in the second idle state may be seen as follows.

Because the number of femtocells in a wireless communication system ispotentially very large, and because there may be practical (or other)limitations to the number of individual base stations that can connectto the AN-AAA server (or servers), femtocells are typically configuredto operate without a connection to the AN-AAA server. Consequently, whena given femtocell receives a conventionally-generated EVDO accessrequest—i.e., one that includes the AT's ESN but not a unique IMSI—thegiven femtocell cannot resolve the ESN into a unique IMSI the way amacro-type base station can. Instead, according to conventionaloperation the given femtocell assigns a locally-unique IMSI to the ATfrom a local pool of IMSI values (wherein each value is unique withinthe pool), and supplies the assigned IMSI to the PDSN for identificationof the EVDO data connection. However, while the assigned IMSI may beunique among the pool used by the given femtocell, it is not necessarilyunique across all pools of other femtocells. As a result, it is possiblefor two or more different femtocells to establish separate EVDOconnections to the same PDSN using the same IMSI, a condition referredto as “IMSI collision.” When an IMSI collision occurs at a PDSN, the twoor more EVDO data sessions using the same IMSI can be interrupted orsuffer other forms of service degradation. Accordingly, avoidance ofIMSI collisions is desirable.

Understood in this context, the unique IMSI provided to femtocells (orother micro-type base stations) in EVDO access requests from ATsoperating in the second idle state advantageously enables differentfemtocells to establish respective EVDO data connections to the samePDSN without the possibility of IMSI collisions, even though thefemtocells lack connections to the AN-AAA server. It will be appreciatedthat the example embodiment can be extended to include any type of basestation (even a macro-type) that lacks an operational connection to theAN-AAA server, thus making the advantages of embodiments of the presentinvention more generally applicable.

The description of the second idle state of step 106 characterizes theoperational behavior of the AT in that idle state, and in particular themanner in which the AT generates an EVDO access request when thecondition (or conditions) necessitating such a request arises. That is,operation in the second idle state does not necessarily require that theAT will actually send an access request. However, although it is notexplicitly illustrated in the flowchart of FIG. 1, the exampleembodiment can be understood to include a specific step of transmittingan access request to the (micro-type) base station. Thus, whileoperating the second idle state, the AT may transmit an access requestfor an EVDO data session to the femtocell, wherein the access requestincludes the AT's unique IMSI. In this instance, once the requested EVDOsession is established, the AT will transition to operating in an activestate in which, at least, the AT engages in the EVDO data session viathe femtocell. In accordance with the example embodiment, the dataconnection between the femtocell and the PDSN used for the EVDO datasession will have been established using the unique IMSI included in theaccess request.

It may also occur that the AT transitions at step 106 to operating inthe second idle state, but does not actually transmit an access requestto the femtocell while operating in the second idle state. For example,the determination at step 104 that leads to the transition of step 106could be responsive to an idle-state handoff of the AT from a macro-typebase station to a femtocell (or other form of micro-type base station),as described above. While not explicitly illustrated in FIG. 1, it couldthen happen that the AT undergoes a subsequent idle-state handoff fromthe femtocell back to the same (or a different) macro-type base stationwithout having transmitted an access request. In accordance with theexample embodiment, the AT, while operating in the second idle state,would make another determination that any access request it makes willbe sent to a macro-type base station, and would responsively transitionto operating in the first idle state.

Note that the characterization of the first idle state of step 102 interms of the access terminal's particular behavior with respect tosending access requests of either protocol type should not be viewed aslimiting the first idle state to only the described behavior of thatstate. The first state could include other behaviors as well, providedthose other behaviors don't contradict or are not mutually exclusivewith the explicitly-described behavior of the first idle state.Similarly, the characterization of the second idle state of step 106 interms of the access terminal's different behavior with respect tosending access requests of the second protocol type should also not beviewed as limiting the second idle state to only the described behaviorof that state. As with the first idle state, the second idle state couldinclude other behaviors as well, provided those other behaviors don'tcontradict or are not mutually exclusive with the explicitly-describedbehavior of the second idle state.

In the discussion of FIG. 1, as well as in other discussions andexplanations herein, the terms “first” and “second” as applied to “idlestates,” “protocols,” and the like, are used as identifying labels, andnot meant to imply any numerical ordering (although a numerical orderingis not necessarily excluded). It will also be appreciated that the stepsof FIG. 1 are shown by way of example, and that additional and/oralternative steps or alternative ordering of steps could be carried outand still remain within the scope and spirit of the present invention.

FIG. 2 provides a simple illustration of the first and second idlestates, the active state, and the transitions between them. The figureis not meant to represent all possible states and all possibletransitions; just those discussed in connection with FIG. 1 above. Inpanel (a) at the top, an access terminal is operating in the first idlestate 202, wherein operation in the first state is characterized by thedescription above. Responsive to a first determination that any accessrequest the AT makes will be sent to a micro-type base station, theaccess terminal makes a transition 203 to operating in the second idlestate 204, wherein operation in the second state is also characterizedabove. As discussed above, the first determination could correspond tothe AT executing an idle-state handoff to a femtocell (or othermacro-type base station), and transition 203 could in turn representsuccessful completion of that handoff.

Panel (b) reproduces the states and transition of panel (a), and alsodepicts the active state 206 and transition 205 from the second idlestate 204 to the active state 206, as well as transition 207 from thesecond idle state 204 back to the first idle state 202. In accordancewith example embodiment, the active state 206 represents operation ofthe AT once an EVDO data session is established via a femtocell. Thetransition 205 to the active state 206 then corresponds to completion ofthe session setup procedure that results in successful establishment ofthe EVDO data session via the femtocell.

As described above, while operating in the second idle state 204, the ATmay make a second determination that any access request it makes will besent to a macro-type base station and the responsively transition tooperating in the first idle state 202. In accordance with the exampleembodiment, this transition would occur without the AT first havinginitiated a call or session via the femtocell while in the second idlestate 204, and is represented in FIG. 2 by transition 207. As discussedabove, the second determination could correspond to the AT executing anidle-state handoff to a macro-type base station, and transition 207could in turn represent successful completion of that handoff. Also asnoted, the states and transitions depicted in FIG. 2 are not necessarilyintended to represent all possible state or transitions of the AT, norshould they be viewed as limiting with respect to the present inventionor embodiments thereof.

FIG. 3 shows a simplified block diagram of a wireless communicationnetwork 300 that can be operated by a wireless service provider, and inwhich an exemplary embodiment of a method and system for providing aunique IMSI in an access request from an access terminal to a basestation for an IS-856 data session can be employed. Subscribers engagein communications in the wireless communication system via accessterminals, whereby access terminals provide a physical basis forinterfacing with the communication system, and subscribers areassociated with respective access terminals according to subscriberaccount information that is maintained by the system in one or more databases. Accordingly, a subscriber is represented by an associated accessterminal AT 302 in FIG. 3.

As shown, AT 302 communicates over an air interface 303-a with a BTS304, which is then coupled or integrated with a BSC 306. AT 302 is alsoshown as having an air interface 303-b to femtocell 326. Communicativeconnections between the femtocell 326 and network 300 are described inmore detail below. Transmissions over air interface 303-a from BTS 304to AT 302 represent a “forward link” from the BTS to the accessterminal, while transmissions over interface 303-a from AT 302 to BTS304 represent a “reverse link” from the AT. Similarly, transmissionsover air interface 303-b from femtocell 326 to AT 302 represent aforward link from the femtocell to the access terminal, whiletransmissions over interface 303-b from AT 302 to femtocell 326represent a reverse link from the AT. Air interfaces 303-a and 303-brepresent links that could be active concurrently or possibly atdifferent times, depending on the operational state of the AT, itsphysical location with respect to the BTS and the femtocell, and thetype data session it seeks or is engaged in.

BSC 306 is connected to MSC 308, which acts to control assignment of airtraffic channels (e.g., over air interface 303-a,b), and provides accessto wireless circuit-switched services such as circuit-voice andcircuit-data (e.g., modem-based packet data) service. As represented byits connection to PSTN 310, MSC 308 is also coupled with one or moreother MSCs, other telephony circuit switches in the operator's (or in adifferent operator's) network, or other wireless communication systems,thereby supporting user mobility across MSC regions, roaming betweensystems, and local and long-distance landline telephone services.

BSC 306 is also connected to AN-AAA server 312, which supports initiallink-level authentication and authorization for 1X-RTT and EVDO datasessions, as mentioned above. Data transport is provided by way of acommunicative link between the BSC 306 and a PDSN 314, which in turnprovides connectivity with the service provider's core packet-datanetwork 316. Sitting as nodes on network 316 are, by way of example, anauthentication, authorization, and accounting (AAA) server 318, amobile-IP home agent (HA) 320, and a border router BR 322 that providessecure connectivity to internet 324, such as the public Internet. TheAAA server 318 provides network- and service-layer authentication andauthorization support, and could be combined with AN-AAA server 312. BR322 could include a firewall or other security mechanisms. Although notshown, core network 316 could comprise one or more additional switches,routers, and gateways that collectively provide transport andinterconnection among the various entities and networks of network 300.In this context, for instance, core network 316 could be an overlay onor a sub-network of one or more additional networks.

Continuing with the description of FIG. 3, network 300 also includes a“Virtual Private Network” (“VPN”) terminator 328 for terminating secureconnections with authorized devices seeking access via unsecure,external networks such as internet 324. For instance, femtocell 326 mayconnect to internet 324 over a broadband connection 327 (e.g., a cablemodem connection or the like) and then to the VPN terminator 328. Thefemtocell could include a “VPN client” that establishes a secure“tunnel” with a “VPN server” in the VPN terminator such that packet-datacommunications over the secure tunnel between the femtocell and the VPNterminator can then take place securely. As is known in the art, secureVPN tunnels can be implemented according such protocols as “IPsec,”although other mechanisms may be employed.

Assuming a secure VPN connection is established, femtocell 326 may thencommunicate securely with other entities in network 300 by way of theVPN terminator 328. In particular, femtocell 326 may receiveconfiguration and messaging data and other operational parameters fromfemtocell controller 330, which provides similar control and servicesfor other femtocells connected to network 300. Femtocell switch 332 actsas a switch between MSC 308 and VPN terminator 328, enabling accessterminals communicating via femtocells, such as AT 302 via femtocell236, to engage in calls via MSC 308 to other wireless devices, as wellas over the PSTN 310. Media translation between packet-based media dataand circuit-based media data is carried out by media gateway MG 334.Thus, femtocell 326 may transmit packetized data MG 334 (via VPNterminator 328), which in turn translates (or transcodes) the data tocircuit-based media for transmission on PSTN 310, for example. MG 334performs the reverse translation for transmission in the oppositedirection.

It should be understood that the depiction of just one of each networkelement in FIG. 3 is illustrative, and there could be more than one ofany of them, as well as other types of elements not shown. Theparticular arrangement shown in FIG. 3 should not be viewed as limitingwith respect to the present invention. Further, the network componentsthat make up a wireless communication system such as system 300 aretypically implemented as a combination of one or more integrated and/ordistributed platforms, each comprising one or more computer processors,one or more forms of computer-readable storage (e.g., disks drives,random access memory, etc.), one or more communication interfaces forinterconnection between elements and the network and operable totransmit and receive the communications and messages described herein,and one or more computer software programs and related data (e.g.,machine-language instructions and program and user data) stored in theone or more forms of computer-readable storage and executable by the oneor more computer processors to carry out the functions, steps, andprocedures of the various embodiments of the present invention describedherein. Similarly, a communication device such as exemplary accessterminal 302 typically comprises a user-interface, I/O components, acommunication interface, a tone detector, a processing unit, and datastorage, all of which may be coupled together by a system bus or othermechanism. As such, network 300, AT 302, and air interface 303-a,b,collectively are representative of example means of implementing andcarrying out the various functions, steps, and procedures describedherein.

As noted above, the term “base station” will be used herein to refer toa Radio Access Network (RAN) element such as a BTS, a BSC, orcombination BTS/BSC, for instance. The term “radio network controller”(RNC) can also be used to refer to a BSC, or more generally to a basestation. Accordingly, a femtocell may be considered to be form ofmicro-type base station or micro-type RNC. In some arrangements, two ormore RNCs may be grouped together, wherein one of them carries outcertain control functions of the group, such as coordinating handoffsacross BTSs of the respective RNCs in the group. The term controllingRNC (or C-RNC) customarily applies to the RNC that carries out these(and possibly other) control functions.

1. CDMA COMMUNICATIONS

a. Conventional CDMA Communications

In a conventional CDMA wireless network compliant with the well knownIS-2000 standard, each cell employs one or more carrier frequencies,typically 1.25 MHz in bandwidth each, and each sector is distinguishedfrom adjacent sectors by a pseudo-random number offset (“PN offset”).Further, each sector can concurrently communicate on multiple differentchannels, distinguished by “Walsh codes.” In doing so, each channel isallocated a fraction of the total power available in the sector. When anaccess terminal operates in a given sector, communications between theaccess terminal and the BTS of the sector are carried on a givenfrequency and are encoded by the sector's PN offset and a given Walshcode. The power allocated to each channel is determined so as tooptimize the signal to noise characteristics of all the channels, andmay vary with time according to the number of access terminals beingserviced, and their relative positions with respect to the BTS, amongother factors.

Air interface communications are divided into forward linkcommunications, which are those passing from the base station to theaccess terminal, and reverse link communications, which are thosepassing from the access terminal to the base station. In an IS-2000system, both the forward link and reverse link communications in a givensector are encoded by the sector's PN offset and a given Walsh code. Onthe forward link, certain Walsh codes are reserved for use to definecontrol channels, including a pilot channel, a sync channel, and one ormore paging channels (depending on service demand, for example), and theremainder can be assigned dynamically for use as traffic channels, i.e.,to carry user communications. Similarly, on the reverse link, one ormore Walsh codes may be reserved for use to define access channels, andthe remainder can be assigned dynamically for use as traffic channels.

In order to facilitate efficient and reliable handoff of accessterminals between sectors, under IS-2000 an AT can communicate on agiven carrier frequency with a number of “active” sectors concurrently,which collectively make up the AT's “active set.” Depending on thesystem, the number of active sectors can be up to six (currently). Theaccess terminal receives largely the same signal from each of its activesectors and, on a frame-by-frame basis, selects the best signal to use.An AT's active set is maintained in the access terminal's memory, eachactive sector being identified according to its PN offset. The ATcontinually monitors the pilot signals from its active sectors as wellas from other sectors, which may vary in as the AT moves about withinthe wireless communication system, or as other factors cause the AT's RFconditions to change. The AT reports the received signal strengths tothe serving base station, which then directs the AT to update its activeset in accordance with the reported strengths and one or more thresholdconditions. Note that an AT's active set can include a femtocell.

With the arrangement described above, an access terminal can engage incellular voice and/or in packet-data (1X-RTT) communications via either(or both of) a macro-type base station or a femtocell. Referring againto FIG. 3, and taking an originating call or data session from AT 302 asan example, AT 302 first sends an origination request either over airinterface 303-a to the BTS 304 or over air interface 303-b to femtocell326. The BSC 304 sends the request to MSC 308 via BSC 306.Alternatively, femtocell 326 sends the request to MSC 308 via femtocellswitch 332. The MSC then signals back to the BSC or the femtocelldirecting one or the other to assign an air interface traffic channelfor use by the access terminal.

For a voice call, the MSC uses well-known circuit protocols to signalcall setup and establish a circuit connection to a destination switchthat can then connect the call to a called device (e.g., landline phoneor another access terminal). The MG 334 provides media translation ifaccess is via the femtocell.

For a packet-data session, the request conventionally includes a uniqueIMSI associated with AT 320. The BSC or the femtocell signals to thePDSN 314, which negotiates with the access terminal to establish a datalink layer connection, such as a point to point protocol (PPP) link. ThePPP link includes a data-path segment between the BSC or femtocell andthe PDSN, and the IMSI is used to identify this data-path segment. ThePDSN 314 sends a foreign agent advertisement that includes a challengevalue to the access terminal, and the access terminal responds with amobile-IP registration request (MIP RRQ), including a response to thechallenge, which the PDSN forwards to HA 320. The HA then assigns an IPaddress for the access terminal to use, and the PDSN passes that IPaddress via either the BSC or the femtocell to the access terminal.

b. High Rate Packet-Data Communications

Under IS-2000, the highest rate of packet-data communicationstheoretically available on a fundamental traffic channel of the forwardlink is 9.6 kbps, dependent in part on the power allocated to theforward-link traffic channel and the resultant signal to noisecharacteristics. In order to provide higher rate packet-data service tosupport higher bandwidth applications, the industry introduced a new“high rate packet data (HRPD) system,” which is defined by industrystandard IS-856.

IS-856 leverages the asymmetric characteristics of most IP traffic, inwhich the forward link typically carries a higher load than the reverselink. Under IS-856, each access terminal maintains and manages an activeset as described above, but receives forward-link transmission from onlyone active sector at a time. In turn, each sector transmits to all itsactive ATs on a common forward link using time division multiplexing(TDM), in order to transmit to only one access terminal at a time, butat the full power of the sector. As a result of the full-powerallocation by the sector, an access terminal operating under IS-856 can,in theory, receive packet-data at a rate of at least 38.4 kbps and up to2.4 Mbps. The reverse link under IS-856 retains largely the traditionalIS-2000 code division multiplexing (CDM) format, albeit with theaddition of a “data rate control” (DRC) channel used by the AT toindicate the supportable data rate and best serving sector for theforward link.

TDM access on the IS-856 forward link is achieved by dividing theforward link in the time domain into time slots of length 2048 chipseach. At a chip rate of 1.228 Mega-chips per second, each slot has aduration of 1.67 milliseconds (ms). Each time slot is further dividedinto two 1024-chip half-slots, each half-slot arranged to carry a96-chip pilot “burst” (pilot channel) at its center and a Medium AccessControl (MAC) channel in two 64-chip segments, one on each side of thepilot burst. The remaining 1600 chips of each time slot (800 perhalf-slot) are allocated for a forward traffic channel or a forwardcontrol channel, so that any given time slot will carry eithertraffic-channel data (if any exists) or control-channel data. As inIS-2000, each sector in IS-856 is defined by a PN offset, and the pilotchannel carries an indication of the sector's PN offset. Again, a sectorcould correspond to a femtocell.

Operation in an IS-856 compliant communication system may beillustrated, again with reference to FIG. 3. To acquire an EVDO packetdata connection, AT 302 sends a UATI (Universal Access TerminalIdentifier) request to BSC 306 (via BTS 304) over air interface 303-a orto femtocell 326 over air interface 303-b. In response, the AT receivesa UATI, which the access terminal can then use to identify itself insubsequent communications with the BSC or femtocell. The access terminalthen sends a connection-request to the BSC 306 or to femtocell 326.Subsequent procedure depends on whether access is made via a macro-typebase station (e.g., BSC 306) or a micro-type base station (e.g.,femtocell 326).

For access via a macro-type base station, the BSC 306 responds to theconnection-request by invoking a process to authenticate the accessterminal and to have the access terminal acquire a data link. Inparticular, the BSC sends an access request to AN-AAA server 312 (whichmay be different than the AAA server 318). The access request includesthe ESN of AT 302, which by convention is provided by the AT in itsinitial access request to the BSC. The AN-AAA server authenticates theaccess terminal and resolves the ESN into a unique IMSI, which isreturned to the BSC. The BSC 306 then assigns radio resources for thedata session, providing a MAC identifier (“MAC ID”) to the AT foridentifying its time-slot data sent in the forward-link traffic channel,and a Walsh code for a sending data on the reverse-link traffic channel.Further, the BSC signals to the PDSN 312, and the PDSN and accessterminal then negotiate to establish a PPP data link. As with a 1X-RTTconnection the IMSI is used to identify the data-path segment betweenthe BSC and the PDSN. The access terminal then sends an MIP RRQ to thePDSN, which the PDSN forwards to the HA 320, and the HA assigns amobile-IP address for the access terminal to use.

As discussed above, a femtocell does not typically maintain a connectionto the AN-AAA server. In conventional operation, access via a macro-type(e.g., femtocell 326) therefore does not include authentication andauthorization by the AN-AAA server, and consequently the AT's ESN cannotbe resolved into a unique IMSI. Instead, the femtocell assigns an IMSIto the AT, which is then used in negotiating the PPP link. As a result,the data-path segment between the femtocell and the PDSN is identifiedusing the assigned IMSI. Again, the access terminal then sends an MIPRRQ to the PDSN, which the PDSN forwards to the HA 320, and the HAassigns a mobile-IP address for the access terminal to use.

Once the access terminal has acquired an IS-856 radio link, a data link,and an IP address, the access terminal is considered to be in an activemode. In active mode, the AT receives its data distributed acrossMAC-identified time slots transmitted by the BTS of femtocell using thefull power of the forward link of the sector selected by the AT (asdescribed above). Thus, the access terminal recognizes its time-slotdata from among other time slots by a MAC identifier included in eachtransmission, and processes only those time slots with the AT's assignedMAC identifier. Using the full power of the forward link maximizes thesignal to noise ratio, thus facilitating higher rate data communicationthan the power-limited CDMA channels. Upon termination of the AT's EVDOsession, the AT returns to an idle or dormant mode of operation.

2. INCLUDING AN IMSI IN ACCESS REQUESTS TO A FEMTOCELL FOR AN EVDO DATASESSION

A typical femtocell may be approximately the size of a desktop phone orWiFi access point, and is essentially a low-power, low-capacity versionof a macro-type base station. Thus, a typical femtocell will use anormal power outlet, perhaps with a transformer providing a DC powersupply. The femtocell may have a wired (e.g., Ethernet) or wireless(e.g., WiFi) connection with a subscriber's broadband connection via aresidential router or other broadband interface. As described above, afemtocell may establish a secure VPN to a VPN terminator in theprovider's core network, and thereby be able to securely communicate viathe VPN terminator with other entities on that core network and beyond.

The femtocell also has a wireless-communication (e.g., CDMA) interfacethat is compatible with the subscriber's access terminal(s), such thatthe femtocell may act as a micro-type base station, providing coveragein the wireless-service provider's network via the subscriber's Internetconnection. Usually, a femtocell will provide service on a single RFcarrier per air interface (e.g., 1X-RTT and EVDO), and also transmit itsown pilot signal.

a. Operating Principles

Both 1X-RTT and EVDO data sessions include a data-path segment betweenthe base station and the PDSN that supports a PPP link between theaccess terminal and the PDSN. In accordance with a CDMA family ofprotocols, including IS-2000 and IS-856, the communicative connectionbetween the base station and the PDSN is designated the “A10/A11interface.” For a macro-type base station, physical link (or links) ofthe A10/A11 interface is generally accommodated entirely within the RAN,as represented by the single connection between BSC 306 and PDSN 314 inFIG. 3, for instance. (The A10/A11 interface is actually defined betweenthe PDSN and a “Packet Control Function,” or “PCF,” configured betweenthe BSC the PDSN. For the purposes of the discussion herein, however,there is no loss in generality with respect to the present invention orembodiments thereof to omit explicit reference to the PCF and considerthe A10/A11 as being between the BSC and the PDSN.) For a femtocell (orother micro-type base station), the physical link (or links) of theA10/A11 interface traverses a VPN tunnel between the femtocell and a VPNterminator in the RAN, as discussed above also in connection with FIG.3. For either type of data session, the PDSN identifies the PPP linkthat runs over the A10/A11 interface according to the IMSI of the accessterminal, as noted above.

For a given access terminal, a unique ESN is assigned by themanufacturer, while a unique IMSI is typically assigned by the serviceprovider, usually in conjunction with creation and configuration of andaccount for the subscriber associated with the AT. For instance, theIMSI could be a calling-station ID, such as a phone number or otheridentifier. As such, IMSIs are reusable and the same unique IMSI couldbe assigned by the service provider to different ATs and differenttimes, while ESN are fixed to AT hardware. The association of an IMSIwith a particular AT is typically tracked in one or another database inthe service provider's network. In particular, the AN-AAA servermaintains (among other information) an association between the ESN of agiven AT and the IMSI assigned to the AT.

As described above, an access terminal supplies its unique IMSI inaccess requests for 1X-RTT connections in accordance with protocolrequirements of 1X-RTT. The IMSI in the access request is then used toidentify the A10/A11 connection that is negotiated between either theBSC or the femtocell and the PDSN. Because the IMSI is unique, everyA10/A11 connection established at a given PDSN has a unique IMSIidentifier.

Unlike 1X-RTT, the protocol requirements of EVDO do not specify that anAT's unique IMSI should be included in access requests for EVDO datasessions. Hence, when an AT seeks access for an EVDO data sessionaccording to conventional operation, it includes its ESN but not itsIMSI in the access request. In practice, a macro-type base station thatreceives such a request executes an authentication an authorizationtransaction with the AN-AAA server, supplying the AT's ESN in thetransaction. More specifically, the connection between the BSC and theAN-AAA server is designated as the “A12 interface,” and the transactioncomprises “A12 terminal authentication.” If the A12 terminalauthentication is successful, the AN-AAA server resolves the ESN intothe AT's unique IMSI and returns the unique IMSI to the BSC. The BSC mayin turn establish an A10/A11 connection to the PDSN using the uniqueIMSI.

Femtocells are generally marketed as consumer electronics products.Consequently, the number of femtocells that connect to a serviceprovider's network can greatly exceed the number of macro-type basestations in the service provider's network. For various practicalreasons, among others, the AN-AAA server cannot generally accommodate anA12 interface to each of the potentially large number of the femtocellsconnected to the service provider's network.

Accordingly, operation of a femtocell is adapted to the absence of aconnection to the AN-AAA server by turning off or disabling the A12terminal authentication in the femtocell.

More particularly, when a femtocell receives a conventional EVDO accessrequest from an AT—i.e., one that includes the AT's ESN but not itsIMSI—the femtocell assigns a local IMSI to the AT. In practice, thefemtocell selects an IMSI at random from a local pool of availableIMSIs. The locally-assigned IMSI is then used to identify the A10/A11interface connection between the femtocell and the PDSN. In thisconventional way, femtocells support EVDO session establishment withoutA12 terminal authentication.

Each local IMSI is unique within the local pool, so that two or more (upto the total number in the pool) AT's may each be assigned alocally-unique IMSI by the femtocell. However, local IMSIs are notguaranteed to be unique across different femtocells. Consequently, inconventional operation it is possible for two (or more) differentfemtocells to assign the same IMSI to ATs seeking EVDO connections withthem. If the different femtocells also establish A10/A11 interfaceconnections with the same PDSN, those connections will not have uniqueIMSI identifiers. As noted above, this situation is called IMSIcollision, and can result in termination of one or all of the EVDOsessions having the same IMSI, or other service degradation. It wouldclearly be desirable to eliminate IMSI collisions that can arise inconventional operation.

Accordingly, an example embodiment of the present invention provides amethod and means for an IMSI to be included in an EVDO access request,and for an A10/A11 interface connection between a micro-type basestation (or any base station that does not perform A12 terminalauthentication) and a PDSN to be established and identified using theIMSI included in the EVDO access request. More particularly, an accessterminal will include its unique IMSI in EVDO access requests tofemtocells, and a femtocell receiving an EVDO access request containingthe AT's IMSI will use this IMSI instead assigning a local IMSI.Advantageously, IMSI collisions on A10/A11 interface connections betweenfemtocells and PDSNs for EVDO data sessions will be eliminated. Theexample embodiment is described below.

b. Access Terminal Operation

In accordance with the example embodiment, when an access terminaloperating in an idle state sends an EVDO access request to its servingbase station, the AT will determine (or will have previously determined)whether its serving base station is macro-type base station or amicro-type base station. If the serving base station is a macro-typebase station, the AT will generate and transmit an access requestaccording to protocol convention for EVDO; i.e., an access request thatomits the AT's IMSI. If, instead, the serving base station is amicro-type base a femtocell (or other micro-type base station), the ATwill generate and transmit an EVDO access request that includes the AT'sunique IMSI. Advantageously, this will allow the receiving femtocell toestablish a uniquely-identified A10/A11 connection with a PDSN, andthereby eliminate possible IMSI collision. When sending a 1X-RTT accessrequest, the AT will operate according to protocol convention, since1X-RTT access requests include the IMSI.

Since the AT has different idle-state behavior with respect to accessrequests depending on the type of its current serving base station, itsoperation may be viewed as describing two different idle states. In thefirst idle state, the AT's serving base station is a macro-type basestation and the AT operates conventionally with respect to both 1X-RTTand EVDO access requests. In the second idle state, the AT's servingbase station is a micro-type base station and the AT then includes itsIMSI in EVDO access requests. This description corresponds with theearlier discussion of FIGS. 1 and 2.

The AT may determine the type (macro or micro) of its serving basestation based on information supplied by the RAN. More particularly,when an access terminal begins operation in a wireless communicationsystem, it first “acquires” the system by listening for a pilot signaland then registering with the base station (or sector, for example) thatemits the strongest detected pilot signal (details of system acquisitionand registration are well known, and not discussed here in detail; thesimplified explanation herein should not be viewed as limiting withrespect the present invention or embodiments thereof). Once the ATacquires the system and registers, it begins operating in an idle state.In this state, the AT can initiate outgoing calls and/or data sessions,and receive alerts of incoming calls and other “overhead” (e.g.,informational) messages from the RAN by periodically listening to one ormore paging and/or control channels. The AT may also hand off from asource base station to a target base station while operating in an idlestate. Upon execution of such an idle-state handoff, the AT monitors thepaging channel of the target base station.

Among the overhead messages that an AT can receive as part of theregistration process or by monitoring its paging channel is a SystemsParameters Message. The System Parameters Message includes (among otherinformation) an ID that identifies the base station or a RAN or RANsubnetwork to which the base station belongs. In accordance with theexample embodiment, the AT will use the identifier in the SystemsParameter Message in order to determine whether the base station is amacro-type base station or a micro-type base station.

More specifically, the service provider can configure the identifiers(and the base stations to which they apply) in such a manner thatcertain ranges of identifier values are associated with macro-type basestations, while other ranges are associated (or reserved forassociation) with micro-type base stations (e.g., femtocells). Further,the AT can be provided or configured with the ID range information. Inthis way, the AT can determine the range to which the identifier in theSystem Parameters Message belongs, and hence determine whether the basestation is a macro-type base station or a micro-type base station.Because the AT receives the System Parameters Message upon registration,and also periodically on the paging channel, the AT will be able todetermine at such time that it makes an EVDO access request which typeof base station will be receiving its access request. In accordance withthe example embodiment, the AT will include its IMSI in an accessrequest to a femtocell, and omit its IMSI in an access request to amacro-type base station.

It will be appreciated that the example embodiment can be extended toinclude any type of base station that lacks an A12 interface or forwhich A12 terminal authentication is turned off or disabled. Thus, theID ranges used to distinguish macro-type base stations from femtocellscould additionally or alternatively distinguish base stations having A12terminal authentication enabled from those having A12 terminalauthentication disabled. Advantageously, the AT can then make adetermination to include its IMSI in EVDO access requests to basestations having A12 terminal authentication disabled, while transmittingconventional EVDO access requests otherwise. It will also be appreciatedthat a message other than a System Parameters Message may be used toprovide an access terminal with information that allows it to determinethe type of its serving base station.

c. Micro-Type Base Station Operation

In further accordance with the example embodiment, a micro-type basestation that receives an EVDO access request including an IMSI willestablish an A10/A11 interface connection to an appropriate PDSN usingthe included IMSI. By so doing, the micro-type base station will ensurethat the A10/A11 interface connection for the EVDO session is uniquelyidentified, just as it would be if A12 terminal authentication had beencarried out. Thus, numerous femtocells widely deployed and connected toa service provider's network (e.g., via secure VPNs as described above)can all support establishment of uniquely-identified A10/A11 connectionsfor EVDO session to any number of PDSN in the service provider'snetwork. At that same time, any practical limitations to supporting anA12 interface between each of numerous femtocells and the AN-AAA serverdo not have to be overcome as a means of eliminating IMSI collisions forEVDO data sessions.

A micro-type base station that receives either a 1X-RTT access requestor an EVDO access request that does not include an IMSI will behaveaccording to protocol convention. Thus, IMSI collisions could stillarise if an access terminal making an EVDO access request fo a femtocelldoes not include its IMSI in the access request. However, byimplementing the example embodiment in most, if not all, ATs andfemtocells, the possibility of IMSI collisions can be significantlyreduced.

3. IMPLEMENTATION OF EXAMPLE EMBODIMENT

As described above, the example embodiment involves actions andoperations carried out by both the access terminal and the micro-typebase station (e.g., femtocell). As such, the example embodiment may beconsidered as comprising a “client-side,” associated with the accessterminal (or other client communication device), and a “system-side,”associated with the femtocell. The example embodiment can be implementedas executable steps and operations of a client-side method carried outby an access terminal, and as executable steps and operations of asystem-side method carried out by a femtocell.

Implementation of the example embodiment can further be considered asincluding means for carrying out both the client-side method and thesystem-side method. An example implementation of both the client-sidemethod and means and the system-side method and means is describedbelow. By way of example, both the access terminal and the femtocell aretaken to be configured to operate according to a CDMA family ofprotocols, including IS-2000 and IS-856, in a similarly-compliantwireless communication system, such as the one described above inconnection with FIG. 3.

a. Example Method Implementation in an Access Terminal

FIG. 4 is a logical flowchart representing executable steps andoperations that could be carried out by an access terminal to implementa client-side method of including an IMSI in an EVDO access request. Theillustrated steps could be implemented in an AT (or similar device) asexecutable instructions stored in the memory of the AT and executed byone or more processors of the AT.

The process as illustrate begins at start 401, wherein the AT may beconsidered to be in an idle state. As such, the AT has identified aserving base station, and is monitoring the paging channel from thatbase station.

At step 402, the AT invokes initiation of an EVDO data session. Thisaction could be carried out in response to a subscriber requesting sucha session, for example by pressing an appropriate combination of keys onthe AT or invoking a data application, such as email or a browser.

The AT selects a base station from which to seek access at step 403. InFIG. 4, the more general designation “Access Node” is used for basestation. In accordance with the example embodiment, the selected accessnode would be the AT's serving base station. Thus the selection could beconsidered as having been made when the AT selected its serving basestation (e.g., as a result of an idle-state handoff).

At step 404, the AT determines whether the access node is a femtocell ora macro-type base station. In further accordance with the exampleembodiment, the AT will consult an “Access Node Type Table” 405 to makethis determination. This table could contain an association of ID rangeswith base station types, as described above. By way of example in FIG.4, macro-type base stations are associated with “ID Range 1” whilefemtocells are associated with “ID Range 2” in the table.

If the access node is a femtocell (“Femtocell” branch from step 404),the AT includes its IMSI in the access request, as indicated at step406. This corresponds to an EVDO access request that advantageouslyprovides the femtocell with a unique IMSI, as described above. Ifinstead the access node is a macro-type base station (“Macro BaseStation” branch from step 404), the AT omit its IMSI from the accessrequest, as indicated at step 407. This corresponds to a conventionalEVDO access request.

Either of steps 406 or 407 then leads to step 408, wherein the AT sendsthe EVDO access request to the access node as part of the process ofnegotiating and EVDO data session with the RAN. If the access node is afemtocell, the EDVO session established in accordance with the exampleembodiment will thereby have a unique IMSI identifier for the A10/A11interface connection between the access node and the PDSN, just as itdoes for a conventionally-established EVDO session via a macro-type basestation. It will be appreciated that the steps shown in FIG. 4 are meantto illustrate operation of the example embodiment. As such, varioussteps could be altered or modified, the ordering of certain steps couldbe changed, and additional steps could be added, while still achievingthe overall desired operation.

b. Example Method Implementation in a Base Station

FIG. 5 is a logical flowchart representing executable steps andoperations that could be carried out by micro-type base station toimplement a system-side method of including an IMSI in an EVDO accessrequest. The illustrated steps could be implemented in a femtocell asexecutable instructions stored in the memory of the femtocell andexecuted by one or more processors of the femtocell.

The process as illustrate begins at start 501, wherein the femtocell maybe acting as a serving base station (or access node) for one or moreaccess terminals.

At step 502, the femtocell receives an access request from an AT for anEVDO data session. The femtocell then determines at step 503 if an IMSIis included in the access request. If an IMSI is included (“Yes” branchfrom step 503), the femtocell negotiates an A10/A11 interface connectionwith the PDSN using the included IMSI. Once the EVDO session isestablished, the process is complete, as represented by the end block515. Thus, in accordance with the example embodiment, the A10/A11interface connection established for the requested EVDO data session hasa unique identifier without the need for A12 terminal authentication toresolve the AT's ESN into its IMSI.

If at step 503 the IMSI is not included (“No” branch from step 503), thefemtocell then determines at step 505 if there is an active A12interface to the AN-AAA server. That is, the femtocell determines if A12terminal authentication is turned on (enabled). If A12 terminalauthentication is enabled (“Yes” branch from step 505), the femtocellexecutes the authentication and receives the AT's IMSI from the AN-AAAserver as indicated at step 507. Then at step 509, the femtocellnegotiates an A10/A11 interface connection with the PDSN using the IMSIreturned from the AN-AAA server. When the EVDO session is established,the process is complete, again as represented by the end block 515. Thisbranch of the process corresponds to conventional establishment of anEVDO session when A12 terminal authentication is enabled.

If it is determined at step 505 that A12 terminal authentication is notenabled (“No” branch from step 505), the femtocell assigns an IMSI froma local pool of IMSIs as indicated at step 511. The pool could be storedin the some form of memory (e.g., solid state, disk, etc.) associatedwith the femtocell, and assignment could be done as a random selectionfrom the pool. At step 513, the femtocell then negotiates an A10/A11interface connection with the PDSN using the assigned IMSI. When theEVDO session is established, the process is complete, once more asrepresented by the end block 515. This branch of the process correspondsto conventional establishment of an EVDO session via a femtocell whenA12 terminal authentication is not enabled.

As discussed above, A12 terminal authentication is typically not turnedon for femtocells, but it could possibly be turned on in some instancesor for some particular femtocells. So the determination at step 505accommodates both situations for a femtocell. Further, the presentexample embodiment could be extended to any type of access node or basestation (or RNC). As such the determination at step 505 can be seen asaccommodating any type of base station that might or might not have A12terminal authentication enabled.

It will be appreciated that the steps shown in FIG. 5 are meant toillustrate operation of the example embodiment. As such, various stepscould be altered or modified, the ordering of certain steps could bechanged, and additional steps could be added, while still achieving theoverall desired operation.

c. Example Access Terminal

FIG. 6 is a simplified block diagram depicting functional components ofan example access terminal 602 in which client-side operation ofincluding an IMSI in an EVDO access request may be implemented. Theexample AT 602 could be a cell phone, a personal digital assistant(PDA), a pager, a wired or wirelessly-equipped notebook computer, or anyother sort of device, as represented by AT 302 in FIG. 3 for example. Asshown in FIG. 6, the example AT 602 includes data storage 604,processing unit 610, transceiver 612, communication interface 614,user-interface I/O components 616, and tone detector 618, all of whichmay be coupled together by a system bus 620 or other mechanism.

These components may be arranged to support conventional operation in awireless communication network that is compliant with a CDMA family ofprotocols, such as network 300 illustrated in FIG. 3. The details ofsuch an arrangement and how these components function to provideconventional operation are well-known in the art, and are not describedfurther herein. Certain aspects of AT 602 relevant to including an IMSIin an EVDO access request are discussed briefly below.

Communication interface 614 in combination with transceiver 612, whichmay include one or more antennas, enables communication with thenetwork, including reception paging messages and System ParametersMessages from the serving base station and transmission of both 1X-RTTand EVDO access request, as well as support for other forward andreverse link channels. The communication interface may include a module,such as an MSM™-series chipset made by Qualcomm Inc. of San Diego,Calif., and supports wireless packet-data communications according to aCDMA family of protocols.

Processing unit 610 comprises one or more general-purpose processors(e.g., INTEL microprocessors) and/or one or more special-purposeprocessors (e.g., dedicated digital signal processor, applicationspecific integrated circuit, etc.). In turn, the data storage 604comprises one or more volatile and/or non-volatile storage components,such as magnetic or optical memory or disk storage. Data storage 604 canbe integrated in whole or in part with processing unit 610, as cachememory or registers for instance. In example AT 602, as shown, datastorage 604 is configured to hold both program logic 606 and programdata 608.

Program logic 606 may comprise machine language instructions that defineroutines executable by processing unit 610 to carry out variousfunctions described herein. In particular the program logic,communication interface, and transceiver may operate cooperatively tocarry out logical operation such as that discussed above and illustratedin FIG. 4. Further, program data 608 may be arranged to store the AccessNode Type Table (or a similar data structure), as described above.

It will be appreciated that there can be numerous specificimplementations of an access terminal, such as AT 602, in which theclient-side method of including an IMSI in an EVDO access request couldbe implemented. Further, one of skill in the art would understand how todevise and build such an implementation. As such, AT 602 isrepresentative of means for carrying out a client-side method ofincluding an IMSI in an EVDO access request, in accordance with themethods and steps described herein by way of example.

d. Example Base Station

FIG. 7 is a simplified block diagram depicting functional components ofan example femtocell 702 in which system-side operation of including anIMSI in an EVDO access request may be implemented. As shown in FIG. 7,the example femtocell 702, representative of femtocell 326 in FIG. 3,for instance, includes a transceiver 704, network interface 706, aprocessing unit 714, and data storage 708, all of which may be coupledtogether by a system bus 716 or other mechanism. In addition, the basestation may also include external storage, such as magnetic or opticaldisk storage, although this is not shown in FIG. 7.

These components may be arranged to support conventional operation in awireless communication network that is compliant with a CDMA family ofprotocols, such as network 300 illustrated in FIG. 3. The details ofsuch an arrangement and how these components function to provideconventional operation are well-known in the art, and are not describedfurther herein. Certain aspects of base station 702 relevant toincluding an IMSI in an EVDO access request are discussed briefly below.

Network interface 706 enables communication on a network, such network300, either directly or via an external connection such as VPN over abroadband connection. As such, network interface 706 may take the formof an Ethernet network interface card or other physical interface to abroadband connection to the internet or some other data network, andfurther can support a VPN connection terminated in a communicationnetwork such as network 300, for instance. Further, network interface706 in combination with transceiver 704, which may include one or morefemtocell-scale BTS antennas, enables air interface communication withone or more access terminals, supporting both forward-link andreverse-link CDMA-based transmissions.

Processing unit 714 comprises one or more general-purpose processors(e.g., INTEL microprocessors) and/or one or more special-purposeprocessors (e.g., dedicated digital signal processor, applicationspecific integrated circuit, etc.). In turn, the data storage 708comprises one or more volatile and/or non-volatile storage components,such as magnetic or optical memory or disk storage. Data storage 708 canbe integrated in whole or in part with processing unit 714, as cachememory or registers for instance. As further shown, data storage 708 isequipped to hold program logic 710 and program data 712.

Program logic 710 may comprise machine language instructions that defineroutines executable by processing unit 714 to carry out variousfunctions described herein. In particular the program logic,communication interface, and transceiver may operate cooperatively tocarry out logical operation such as that discussed above and illustratedin FIG. 5.

It will be appreciated that there can be numerous specificimplementations of a femtocell, such as femtocell 702, in which thesystem-side method of including an IMSI in an EVDO access request couldbe implemented. Further, one of skill in the art would understand how todevise and build such an implementation. As such, femtocell 702 isrepresentative of means for carrying out a system-side method ofincluding an IMSI in an EVDO access request, in accordance with themethods and steps described herein by way of example.

4. CONCLUSION

An exemplary embodiment of the present invention has been describedabove. Those skilled in the art will understand, however, that changesand modifications may be made to this embodiment without departing fromthe true scope and spirit of the invention, which is defined by theclaims.

We claim:
 1. In a micro-type base station configured to operate in awireless communication system, and further configured to support dataconnections of both a first protocol type and a second protocol typewith access terminals operating in the wireless communication system, amethod comprising: receiving an access request from an access terminalto initiate a communication session using a data connection of thesecond protocol type, wherein the access request includes a particularidentifier that is one given type of a plurality of types of identifiersthat are each uniquely associated with the access terminal, and whereinthe second protocol type has no specification to include identifiers ofthe given type in access requests for data connections of the secondprotocol type; and establishing a data communication session of thesecond protocol type with the access terminal based at least in part onthe particular identifier included in the access request, wherein themicro-type base is a femtocell station configured to operate accordingto a CDMA family of protocols, including at least 1X-RTT and EVDO,wherein the first protocol type is 1X-RTT, the second protocol type isEVDO, and the particular identifier is an IMSI included in the receivedaccess request, and wherein establishing the data communication sessionof the second protocol type with the access terminal based at least inpart on the particular identifier included in the access requestcomprises associating the IMSI included in the received access requestwith data transmissions between the femtocell and a Packet Data ServingNode in the wireless communication system.
 2. The method of claim 1,further comprising: receiving an access request for a data connection ofthe second protocol type from a different access terminal, the accessrequest not including the particular identifier; assigning a particularidentifier from a local pool of available identifiers; and establishinga data communication session of the second protocol type with the accessterminal based at least in part on the assigned particular identifier.3. The method of claim 2, wherein establishing the data communicationsession of the second protocol type with the access terminal based atleast in part on the assigned particular identifier comprisesassociating the assigned IMSI with data transmissions between thefemtocell and a Packet Data Serving Node in the wireless communicationsystem.
 4. A micro-type base station configured to operate in a wirelesscommunication system, and further configured to support data connectionsof both a first protocol type and a second protocol type with accessterminals configured to operate in the wireless communication system,the micro-type base station comprising: means for receiving an accessrequest from an access terminal to initiate a communication sessionusing a data connection of the second protocol type, wherein the accessrequest includes a particular identifier that is one given type of aplurality of types of identifiers that are each uniquely associated withthe access terminal, and wherein the second protocol type has nospecification to include identifiers of the given type in accessrequests for data connections of the second protocol type; and means forestablishing a data communication session of the second protocol typewith the access terminal based at least in part on the particularidentifier included in the access request, wherein the micro-type basestation is a femtocell configured to operate according to a CDMA familyof protocols, including at least 1X-RTT and EVDO, and wherein the firstprotocol type is 1X-RTT, the second protocol type is EVDO, and theparticular identifier is an IMSI included in the received accessrequest, and wherein establishing the data communication session of thesecond protocol type with the access terminal based at least in part onthe particular identifier included in the access request comprisesassociating the IMSI included in the received access request with datatransmissions between the femtocell and a Packet Data Serving Node inthe wireless communication system.